It is very difficult to find places willing to let people study A-levels past the age of 19, never mind tailored fast track courses - even when you're willing to pay. This means that you can either do ATHE (Which is what you're doing) or distance learning courses (Which generally tend to be expensive - like 500+ an A level for the study material & then you need to sort out your own exams)
In my opinion ATHE is the best way for a mature student to go to university, but if you want to do A levels to get onto a uni course my advice is to study the A levels in your own time. For STEM subjects there is a wealth of study material online, I've managed to teach myself AS & A2 chemistry in 3 1/2 months using nothing but a few secondhand textbooks from amazon, YouTube videos and various free online learning resources - the only part that cost money/was tedious was finding a place to do my practical exams. Learning solo is actually much better because there is no distractions, you can study whenever you like and you can learn in your own style - so long as you have covered everything in the syllabus and fully understand it there is no reason why you can't do as well as somebody who has studied at a college/learning center etc.